<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>盒子模型</title>
    <link href="css/css_06_盒子模型.css" rel="stylesheet">
</head>
<body>
<div class="header">
    <div class="left"></div>
    <div class="medium"></div>
    <div class="right"></div>
</div>
<h1>外间距:200px</h1>
<div class="d1">内间距</div>

</body>
</html>